A method for producing ceramics by low-temperature sintering of ceramic iron-removal waste residues and applications thereof

Abstract

This invention discloses a method and application for producing ceramics using low-temperature sintering of iron removal waste residue, belonging to the field of ceramic product manufacturing technology. The method includes the following steps: (1) Mixing: Iron removal waste residue from the ceramic production process is added to the ceramic raw materials as a sintering aid, mixed evenly, and performance additives and dispersants are added to obtain a mixture; wherein, the amount of iron removal waste residue added is 2-4 wt.% of the total mass of the ceramic raw materials; (2) Molding: The mixture obtained in step (1) is aged under vacuum for 18-24 hours, and then pressed into shape to obtain a ceramic green body for later use; (3) Sintering: The ceramic green body obtained in step (2) is sintered at a temperature of 1060-1100℃ to obtain ceramic products. The method of this invention can be applied in the production of building ceramics or industrial ceramics. This invention has the characteristics of achieving low-temperature sintering of ceramics, and the temperature reduction of 40-80℃ compared with the traditional sintering temperature, resulting in energy saving and consumption reduction.

Description

Technical Field

[0001] This invention pertains to ceramic product manufacturing methods, specifically relating to a method and its application for producing ceramics using low-temperature sintering of iron removal waste slag. Background Technology

[0002] The sintering temperature of building ceramics and daily-use ceramics needs to be as high as 1200℃ or more, which not only consumes a lot of energy such as coal and natural gas, but also causes a lot of carbon dioxide emissions.

[0003] To lower the sintering temperature of ceramics, the industry commonly uses the addition of sintering aids. Traditional sintering aids mainly include the following categories: ① Mineral-based aids, such as zircon sand (ZrSiO4), which offer stable results but are expensive; ② Chemical-based aids, such as barium carbonate (BaCO3) and borates, but these result in ceramic products with low density. Furthermore, traditional sintering aids are all purchased externally by ceramic factories, significantly increasing raw material costs.

[0004] Furthermore, in the production process of pursuing high-quality ceramics (especially white ceramic bodies), "iron removal" is a crucial raw material purification step. The technical means typically employed is to remove iron-containing impurities from the slurry using high-intensity magnetic separation equipment, resulting in a large amount of iron-removed waste residue. This waste residue includes iron minerals such as hematite, limonite, and ilmenite, whose chemical composition is mainly SiO2, Al2O3, and Fe2O3, with small amounts of alkaline oxides such as K2O, Na2O, CaO, and MgO. Iron-removed waste residue, along with waste residues with similar composition and properties to ceramic bodies, is usually treated as solid waste and stockpiled or landfilled, not only wasting resources but also posing a serious risk of environmental pollution.

[0005] Existing research reports have disclosed the use of iron slag from other industries (such as steel slag) in ceramic sintering processes. However, the iron removal waste generated in the ceramic production process itself, and the fact that this iron removal waste is highly compatible with the main components such as SiO2 and Al2O3 in ceramic raw materials, and the ability to use this iron removal waste as a sintering aid in a targeted and specific manner to achieve the synergistic goal of "waste treatment" and energy conservation and consumption reduction in the ceramic sintering system, is still a technological gap. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for producing ceramics using low-temperature sintering of ceramic iron removal waste. This method can be applied in the production of building ceramics or industrial ceramics. This invention involves the targeted recycling of ceramic iron removal waste for low-temperature sintering to prepare ceramic materials. The main component of the recycled waste, Fe2O3, forms a low-temperature eutectic system with SiO2, Al2O3, and flux in the ceramic raw materials during the sintering process. This reduces the sintering temperature to 1060–1100°C, creating a closed-loop material recycling model within the ceramic production process. This achieves near-zero solid waste emissions and significantly reduces raw material costs.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for producing ceramics by low-temperature sintering of iron removal waste residue, the method comprising the following steps: (1) Ingredient mixing: Iron-removing waste residue from the ceramic production process is added to the ceramic raw materials as a sintering aid, mixed evenly, and performance additives and dispersants are added to obtain the mixture; wherein, the amount of iron-removing waste residue added is 2-4 wt.% of the total mass of the ceramic raw materials; (2) Molding: The mixture obtained in step (1) is aged under vacuum for 18-24 hours, and then pressed into shape to obtain ceramic green body for later use. (3) Sintering: The ceramic green body obtained in step (2) is sintered at a temperature of 1060 to 1100°C to obtain ceramic products.

[0008] Furthermore, the main component of the iron removal slag in step (1) is Fe2O3, with a Fe2O3 content of 30% to 40%; the ceramic raw materials include 0.4% bauxite, 2.5% recycled material, 3% BH material, 4.7% fine ceramic tile powder, 9% fine potassium sand, 1.8% polishing slag and glaze slag, 2% fine grinding edge slag, 2.3% silica sand, 36.6% high-sodium stone powder, 3.6% Jiangxi talc mud, 6.0% mixed bentonite, 11% mixed mud paste, 8.1% Mingchuang high-alumina mud, 4.5% gray-black raw mud, and 4.5% base bentonite.

[0009] Furthermore, the performance additives are ceramic body reinforcing agents and liquid desiccant, wherein the amount of ceramic body reinforcing agent added is 0.1 wt.% of the total mass of ceramic raw materials, and the amount of liquid desiccant added is 0.8 wt.% of the total mass of ceramic raw materials; the dispersant is sodium tripolyphosphate, and the amount added is 0.2 to 0.5 wt.% of the total mass of ceramic raw materials.

[0010] Furthermore, in step (1), the iron slag and ceramic raw materials are mixed by ball milling for 8 to 12 hours.

[0011] Further, during the ball milling process, the mass ratio of the primary material, milling media, and water is 1:1.2–2:0.5–1. After milling, the resulting mixed ball mill material is dried at 160°–200°C for 2–2.5 hours, then cooled to room temperature. Next, 8–12 wt.% water is added, and the mixture is then ground through a 20–30 mesh sieve to obtain the lower layer of raw material, thus yielding the final mixture. It should be noted that the primary material is obtained by mixing iron-removing waste slag, ceramic raw materials, performance additives, and dispersants.

[0012] Further, in step (2), the mixture dried to a moisture content of ≤0.5% is replenished with water to adjust the moisture content to 7%–9%, ​​and aged under a vacuum of 0.06–0.08 MPa for 18–24 hours. Through the synergistic effect of moisture swelling and negative pressure, the tiny air bubbles remaining inside the mixture after drying are removed, so that the porosity of the subsequently formed blank is reduced to below 2% and the cracking rate is ≤0.3%. The aging temperature is 25–30℃, and the air bubble removal rate is ≥90%. This improves the plasticity uniformity of the mixture by more than 15%.

[0013] Furthermore, in step (2), the ceramic green body is formed by pressing with a hydraulic press at a pressure of 20-50 MPa.

[0014] Furthermore, in step (3), the sintering process is atmospheric pressure sintering, the heating rate is 3 to 10 °C / min, and the temperature is held at 1060 to 1100 °C for 0.5 to 2 hours.

[0015] The ceramic products prepared by this invention have a water absorption rate of 0.33-0.97%, a bending strength of 55.3 MPa to 57.2 MPa, a shrinkage rate of 6.13-7.64%, and a whiteness of 22.06-23.35%.

[0016] The method for producing ceramics using low-temperature sintering of iron removal waste slag, as described in this invention, can be applied in the production of building ceramics or industrial ceramics. Building ceramics include antique bricks, exterior wall bricks, floor tiles, etc.

[0017] The core principle of this invention lies in utilizing the Fe2O3 and other components abundant in iron removal waste slag, along with SiO2, Al2O3, flux (high-sodium stone powder), and co-solvent components (fine potassium sand, polishing slag, and glaze slag) in the ceramic raw materials, to construct a low-temperature eutectic system during sintering, thereby reducing the sintering temperature to 1060–1100°C. By introducing a "built-in" liquid phase that can be triggered and continuously act at a lower temperature, the sintering process of ceramics is fundamentally changed and optimized, thus achieving low-temperature, efficient, and energy-saving densification sintering without relying on external additives or extremely high temperatures. When this system reaches its eutectic point, it generates an iron-containing low-temperature liquid phase (such as iron olivine Fe2SiO4), which operates through the classic liquid-phase sintering mechanism: the capillary force generated by the liquid phase promotes the rearrangement and initial densification of solid particles, while accelerating mass transport through a "dissolution-precipitation" mechanism, promoting grain growth and porosity elimination, ultimately producing a fully densified ceramic material at a lower temperature.

[0018] The present invention places the mixture obtained in step (1) under a vacuum of 0.06-0.08 MPa and a temperature of 25-30°C for 18-24 hours, which can effectively solve the following four defects: 1. Unaged billets are prone to localized over-drying or over-wetness. During molding, over-dry areas are prone to cracking, while over-wet areas are prone to collapse. Significant differences in moisture evaporation rates during the drying stage can cause warping and cracking of the billet, ultimately leading to product deformation or scrap after sintering. This invention employs aging under vacuum conditions, effectively solving the molding defects caused by uneven moisture content in the billet.

[0019] 2. If clay-based blanks are directly molded, their poor plasticity leads to easy breakage during extrusion molding and difficulty in shaping by hand. This invention, through aging and ion exchange to enhance interparticle lubrication, improves the plasticity of the blank, enabling the smooth molding of complex shapes (such as ceramic pipes and irregularly shaped parts). Therefore, this invention solves the molding and processing problems caused by insufficient plasticity in existing materials.

[0020] 3. During the kneading or mixing process, the raw material particles are subjected to shear force, generating internal stress. If directly dried / sintered, the stress release will lead to microcracks inside the raw material. This invention allows for slow particle displacement during aging, gradually relaxing the stress and preventing crack propagation in subsequent processes. Therefore, this invention solves the problem of drying / sintering cracking caused by residual internal stress.

[0021] 4. Uneven distribution of dispersants and binders can lead to differences in local adhesion strength in the green body, resulting in inconsistent local shrinkage during sintering and the formation of pores, pinholes, or delamination. This invention utilizes vacuum aging, which allows for uniform adsorption of sintering aids, ensuring uniform densification during sintering. This solves the sintering defects caused by uneven distribution of existing sintering aids.

[0022] Compared with the prior art, the significant beneficial effects achieved by the present invention are: 1. This invention reduces the ceramic sintering temperature from the traditional 1140℃ and above to 1060-1100℃, a reduction of 40-80℃. This can reduce energy consumption in the firing process by approximately 7.5%, equivalent to saving approximately 14.6 kg of standard coal per ton of product.

[0023] 2. This invention involves aging the green body under vacuum for 18–24 hours, improving the plasticity and fluidity of the green body. The resulting green body has a high surface smoothness, free from defects such as cracks, collapse, and delamination. It reduces the scrap rate in the forming process; uniform moisture distribution ensures consistent drying rates and uniform drying shrinkage, preventing warping and cracking during drying, shortening the drying cycle, and improving production efficiency. It also enhances the uniformity of the green body composition, ensuring synchronized densification rates during sintering without localized over- or under-firing; eliminating residual internal stress; resulting in uniform density of the sintered product; and improving mechanical properties (flexural strength, hardness) by 10%–30%. Simultaneously, it reduces defects such as porosity and pinholes, significantly improving the appearance quality and performance stability of ceramic products. For plastically formed green bodies of high-purity oxide ceramics (such as alumina and zirconium oxide) or non-oxide ceramics (such as silicon nitride), aging can significantly improve the uniformity of the green body, laying the foundation for subsequent sintering to prepare high-density, high-performance ceramic components.

[0024] 3. This invention uses iron removal slag as a sintering aid, achieving a "zero-cost" substitution of raw materials by replacing purchased aids with its own slag. It also saves on slag disposal costs, solving the problem of treating iron removal slag as solid waste and stockpiling or landfilling it. Furthermore, it enables the recycling of iron removal slag, thus resolving the environmental pollution caused by existing iron removal slag stockpiling or landfilling. In summary, the cost of producing one ton of ceramic products using this invention is approximately 337.5 yuan lower than existing production processes, significantly reducing production costs and improving economic efficiency.

[0025] 4. This invention ensures that ceramic products can still achieve high densification at low temperatures through a liquid-phase sintering mechanism, and their key physical properties such as flexural strength and bulk density can meet or exceed the standard requirements.

[0026] 5. This invention transforms solid waste from iron slag into functional additives, constructing a closed-loop production model of "waste-raw material," achieving "near-zero emissions" of solid waste from the source, and developing a new type of clean production and circular economy technology model. Attached Figure Description

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0028] Figure 1The curves showing the change in bulk density of ceramic products prepared in Comparative Example 1, Example 1, and Example 2 as a function of sintering temperature are shown.

[0029] Figure 2 The curves showing the change in water absorption rate with sintering temperature for the ceramic products prepared in Comparative Example 1, Example 1, and Example 2 are shown.

[0030] Figure 3 The curves showing the change in flexural strength as a function of sintering temperature for the ceramic products prepared in Comparative Example 1, Example 1, and Example 2 are shown.

[0031] Figure 4 The linear shrinkage rate of the ceramic products prepared in Comparative Example 1, Example 1, and Example 2 is shown as a function of sintering temperature.

[0032] Figure 5 This is a comparison chart of the whiteness of ceramic products prepared in Comparative Example 1, Example 1, Example 2 and Example 3.

[0033] Figure 6 For comparison of the XRD patterns of ceramic products prepared in Comparative Example 1, Example 1 and Example 2.

[0034] Figure 7 This is a comparison diagram of the microstructures of Comparative Example 1 and Example 1. In the diagram, Figure 7 a is a microstructure diagram of Comparative Example 1 after sintering at 1140℃; Figure 7 b is a microstructure diagram of Example 1 sintered at 1080°C; Figure 7 c shows that the sample of Comparative Example 1 has a large number of wrinkles on the particle surface; Figure 7 d shows the sample of Example 1, whose particle surface became unusually smooth.

[0035] To facilitate understanding of the accompanying figures, the following explanations are provided for the standardized labeling used in the figures: "Standard line": This represents the acceptable threshold or industry standard requirement for the performance of ceramic products. In the illustration, it is represented by an orange dashed line, and the area indicated by the arrow is the acceptable area.

[0036] Sample naming rules: S2, S4, S5: The numbers represent the mass percentage of the added iron removal slag, which are 2%, 4%, and 5%, respectively.

[0037] S2-1080: This indicates that a sample with 2% added iron removal slag was sintered at 1080℃. This naming convention applies to all similar labels. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] The ceramic products prepared in this embodiment of the invention are antique-style brick products. The ceramic raw material formula includes the following components by mass percentage: bauxite 0.4%, recycled material 2.5%, hard body material 3%, fine ceramic tile powder 4.7%, fine potassium sand 9%, polishing residue and glaze residue 1.8%, fine edge grinding residue 2%, silica sand 2.3%, high sodium stone powder 36.6%, Jiangxi talc mud 3.6%, mixed bentonite 6.0%, mixed mud paste 11%, Mingchuang high alumina mud 8.1%, gray-black raw mud 4.5%, and base material bentonite 4.5%.

[0040] The mass ratio of polishing residue to glaze residue is 1:0.8 to 1. For example, if the polishing residue is 1%, the glaze residue is 0.8%. Or, if the polishing residue is 0.9%, the glaze residue is 0.9%.

[0041] The content of SiO2 in ceramic raw materials can reach 40% to 50%, and the content of Al2O3 can be 20% to 30%.

[0042] The iron slag contains substances such as Fe2O3, Al2O3, and SiO2, with Fe2O3 accounting for 30% to 40%.

[0043] Example 1: A method for producing ceramics using low-temperature sintering of iron removal waste slag includes the following steps: (1) Ingredient mixing: Weigh 300g of raw materials according to the ceramic raw material formula, then add 4% by mass of iron-removing waste residue, sodium tripolyphosphate, Yueyang ceramic body strengthening agent and liquid desiccant. The amount of sodium tripolyphosphate added is 0.3% of the total mass of ceramic raw materials, and sodium tripolyphosphate is used as a dispersant; the amount of Yueyang ceramic body strengthening agent added is 0.1% of the total mass of ceramic raw materials, and the amount of liquid desiccant added is 0.8% of the total mass of ceramic raw materials. The ingredients, ball milling media and water are mixed in a mass ratio of 1:1.2:0.5. After weighing, put the raw materials into a ball mill jar and ball mill for 8 hours, then put them into an oven at 160℃ and dry for 2.5 hours. Take out the raw materials and cool them to room temperature.

[0044] (2) Molding: Then, 8wt% deionized water was added and the mixture was ground through a 20-mesh sieve to obtain the lower layer of raw material. The lower layer of raw material was aged under vacuum for 18 hours. The aging temperature was 25℃, and the bubble removal rate was ≥90%. Under these conditions, the water penetration rate was good, which improved the plasticity and uniformity of the mixture by more than 15%. After aging, 30g of the raw material was weighed each time, placed in a mold, and pressed into shape under an electric hydraulic sample making machine to obtain 10 samples.

[0045] The pre-aging process includes: drying the mixture to a moisture content of ≤0.5% (obtained by ball milling and drying), adding deionized water to adjust the moisture content to 7%, and aging it under a vacuum of 0.06MPa for 18 hours. Through the synergistic effect of moisture swelling and negative pressure, the tiny air bubbles remaining after drying in the mixture are removed, reducing the porosity of the subsequently formed blank to below 2% and the cracking rate to ≤0.3%.

[0046] (3) Sintering: After molding, the samples were dried for 2 hours. Then, 7 samples (the remaining 3 samples were used as supplements to avoid defective samples) were placed in a programmable temperature gradient furnace and sintered at atmospheric pressure at 7 temperature levels: 1040℃, 1060℃, 1080℃, 1100℃, 1120℃, 1140℃, and 1160℃. The heating rate was 5℃ / min, and the highest temperature was held for 1 hour to prepare ceramic products with 4% iron-removed waste residue added at different sintering temperatures. The ceramic products were then characterized and their performance was tested.

[0047] Example 2: A method for producing ceramics using low-temperature sintering of iron removal waste slag includes the following steps: (1) Ingredient mixing: Weigh 300g of raw materials according to the ceramic raw material formula, then add 2% by mass of iron-removing waste residue, sodium tripolyphosphate, Yueyang ceramic body strengthening agent and liquid desiccant. The amount of sodium tripolyphosphate added is 0.3% of the total mass of ceramic raw materials, and sodium tripolyphosphate is used as a dispersant; the amount of Yueyang ceramic body strengthening agent added is 0.1% of the total mass of ceramic raw materials, and the amount of liquid desiccant added is 0.8% of the total mass of ceramic raw materials. The ingredients, ball milling media and water are mixed according to a mass ratio of 1:1.6:0.75. After weighing, put the raw materials into a ball mill jar and ball mill for 10 hours, then put them into an oven at 180℃ and dry for 2.3 hours. Take out the raw materials and cool them to room temperature.

[0048] (2) Molding: Then, 10wt% deionized water was added and the mixture was ground through a 25-mesh sieve to obtain the lower layer of raw material. The lower layer of raw material was aged under vacuum for 19 hours. The aging temperature was 27℃, and the bubble removal rate was ≥93%. Under these conditions, the water penetration rate was good, which improved the plasticity uniformity of the mixture by more than 18%. After aging, 30g of the raw material was weighed each time, placed in a mold, and pressed into shape under an electric hydraulic sample making machine to obtain 10 samples.

[0049] The pre-aging process includes: drying the mixture to a moisture content of ≤0.5% (obtained by ball milling and drying), adding deionized water to adjust the moisture content to 8%, and aging it under a vacuum of 0.07MPa for 21 hours. Through the synergistic effect of moisture swelling and negative pressure, the tiny air bubbles remaining after drying in the mixture are removed, reducing the porosity of the subsequently formed blank to below 2% and the cracking rate to ≤0.2%.

[0050] (3) Sintering: After molding, the samples were dried for 2 hours. Then, 7 samples (the remaining 3 samples were used as supplements to avoid defective samples) were placed in a programmable temperature gradient furnace and sintered at atmospheric pressure at 7 temperature levels: 1040℃, 1060℃, 1080℃, 1100℃, 1120℃, 1140℃ and 1160℃. The heating rate was 5℃ / min, and the highest temperature was held for 1 hour. Ceramic products with 2% iron removal waste residue added at different sintering temperatures were prepared, and the ceramic products were characterized and their performance was tested.

[0051] Example 3: A method for producing ceramics using low-temperature sintering of iron removal waste slag includes the following steps: (1) Ingredient mixing: Weigh 300g of raw materials according to the ceramic raw material formula, then add 5% by mass of iron-removing waste residue, sodium tripolyphosphate, Yueyang ceramic body strengthening agent and liquid desiccant. The amount of sodium tripolyphosphate added is 0.3% of the total mass of ceramic raw materials, and sodium tripolyphosphate is used as a dispersant; the amount of Yueyang ceramic body strengthening agent added is 0.1% of the total mass of ceramic raw materials, and the amount of liquid desiccant added is 0.8% of the total mass of ceramic raw materials. Mix the ingredients, ball milling media and water in a mass ratio of 1:2:1. After weighing, put the raw materials into a ball mill jar and ball mill for 12 hours, then put them into an oven at 200℃ and dry for 2 hours. Take out the raw materials and cool them to room temperature.

[0052] (2) Molding: Then, 12wt% deionized water was added and the mixture was ground through a 30-mesh sieve to obtain the lower layer of raw material. The lower layer of raw material was aged under vacuum for 19 hours. The aging temperature was 30℃, and the bubble removal rate was ≥95%. Under these conditions, the water penetration rate was good, which improved the plasticity and uniformity of the mixture by more than 20%. After aging, 30g of the raw material was weighed each time, placed in a mold, and pressed into shape under an electric hydraulic sample making machine to obtain 10 samples.

[0053] The pre-aging process includes: drying the mixture to a moisture content of ≤0.5% (obtained by ball milling and drying), adding deionized water to adjust the moisture content to 9%, and aging it under a vacuum of 0.08MPa for 24 hours. Through the synergistic effect of moisture swelling and negative pressure, the tiny air bubbles remaining after drying in the mixture are removed, reducing the porosity of the subsequently formed blank to below 2% and the cracking rate to ≤0.2%.

[0054] (3) Sintering: Seven samples (the remaining three were used as supplementary samples to avoid defective samples) were placed in a programmable temperature gradient furnace and sintered at atmospheric pressure at seven temperature settings: 1040℃, 1060℃, 1080℃, 1100℃, 1120℃, 1140℃, and 1160℃. The heating rate was 10℃ / min, and the highest temperature was maintained for 2 hours to prepare ceramic products with 5% iron-removed waste residue added at different sintering temperatures. The ceramic products were then characterized and their performance was tested.

[0055] Comparative Example 1: The only difference from Example 1 is that no additional iron-removing waste slag (0%) was added to the ceramic raw material formula. Multiple blanks were prepared and placed in a programmable temperature gradient furnace. Seven temperatures were set at 1040℃, 1060℃, 1080℃, 1100℃, 1120℃, 1140℃, and 1160℃ for atmospheric pressure sintering. Ceramic products with 0% iron-removing waste slag added at different sintering temperatures were obtained and characterized and tested.

[0056] Material performance testing The structural and performance characterization analyses of the products prepared in Examples 1-3 and Comparative Example 1 (hereinafter referred to as "samples") are as follows: (a) Macroscopic physical performance testing (1) Bulk density: This experiment used a solid density balance (MZ-324SD model) provided by Shenzhen Miaozhun Technology Co., Ltd. to determine the bulk density of materials based on Archimedes' principle. Before testing, all samples were dried at 160℃ for 2 hours and then placed in the solid density balance for density measurement. The samples must be completely immersed in the liquid for 30 seconds to allow the readings to fluctuate within a small range, ensuring the accuracy of the measured bulk density. The calculation results are as follows: Figure 1 As shown.

[0057] like Figure 1 As shown, before the sintering temperature reached 1140℃, the bulk density of all samples remained above the acceptable standard of 2.4 g / cm³. It is noteworthy that the bulk density of the samples showed a slight decreasing trend with the increase of the amount of iron-removing waste residue added, possibly due to the difference between the theoretical density of the introduced waste residue and the basic ceramic raw materials.

[0058] Depend on Figure 1Furthermore, it can be seen that, using the method of the present invention, at a sintering temperature of 1060℃, the density values ​​of sample S2 obtained by adding 2% iron removal slag and sample S4 obtained by adding 4% iron removal slag both exceeded the usage requirements (bulk density 2.4 g / cm³), fully demonstrating the feasibility of applying the present invention with iron removal slag at lower temperatures. When the sintering temperature exceeded 1140℃, the bulk density of all samples showed a precipitous drop. This indicates the occurrence of over-firing; excessively high temperatures lead to an excess of liquid phase in the green body, which may cause abnormal grain growth, aggregation and expansion of closed pores, or macroscopic deformation of the product.

[0059] Table 1. Bulk density (g / cm³) of samples at different sintering temperatures

[0060] As shown in Table 1, although the density value of the sample of the present invention is smaller than that without the addition of iron removal slag, it still exceeds the usage requirements (bulk density 2.4 g / cm³), indicating the feasibility of the present invention in adding iron removal slag at lower temperatures (meets the usage requirements), realizing the recycling of waste materials, overcoming the problem of iron removal slag needing to be stockpiled or landfilled, and greatly reducing the risk of environmental pollution.

[0061] (2) Water absorption rate: This experiment used the ZH10901 ceramic water absorption vacuum device provided by Foshan Yidian Experimental Instrument Co., Ltd. to determine the water absorption rate of ceramic products.

[0062] The test conditions were as follows: the evacuation time to reach 10 kPa was less than 10 minutes. The maximum size of the material placed was 200×200×10 mm, and no more than 15 pieces were allowed. The material was placed in the ZH10901 ceramic water absorption vacuum device for 1 hour. The water absorption rate of the material was calculated based on the mass change before and after water absorption using the following formula:

[0063] In the formula, W represents the water absorption rate of the material (%), M1 represents the mass of the material before water absorption (g), and M2 represents the mass of the material after water absorption (g).

[0064] like Figure 2 As shown, the water absorption rate of the comparative sample S0 prepared in Comparative Example 1 without the addition of iron removal slag gradually decreased with increasing sintering temperature, reaching its lowest value (0.072%) at 1140℃, which meets the superior grade standard (water absorption rate ≤ 0.1%). This indicates that the original formula of Comparative Example 1 must rely on high temperature to achieve sufficient sintering.

[0065] After adding iron removal waste residue, the sintering behavior of sample S4 in Example 1 and sample S2 in Example 2 underwent fundamental changes. In Example 1, 4% iron removal waste residue was added, and sample S4 reached its lowest water absorption rate (0.037%) at 1060℃. In Example 2, 2% iron removal waste residue was added, and sample S2 reached its lowest water absorption rate (0.039%) at 1080℃.

[0066] The above results show that the present invention (with the addition of iron slag at a rate of 2 wt.% and 4 wt.%) can significantly advance and broaden the ceramic sintering temperature window in the prior art from the traditional 1140℃ to a low-temperature range of 1060 to 1080℃.

[0067] (3) Flexural strength: Flexural strength refers to the ultimate breaking stress of a material when subjected to bending per unit area. The ultimate stress can be calculated based on the bending moment and the section modulus of the material's cross-section.

[0068] The testing method employed was the three-point bending method. The fired ceramic material was smoothed with sandpaper, and the width and thickness were measured three times using electronic vernier calipers. The average value was then taken, and the flexural strength was determined using the national standard three-point bending method on a program-controlled flexural strength tester. The tester's span L was 80 mm, and the loading speed was 0.4 mm / min. The calculation formula for the flexural strength determined by the three-point bending method is as follows:

[0069] In the formula, P represents the flexural strength of the material (MPa), F represents the maximum load when the specimen breaks (N), L represents the distance between the specimen supports (mm), b represents the width of the specimen fracture (mm), and h represents the thickness of the specimen fracture (mm).

[0070] like Figure 3 As shown, the peak intensity of the undoped sample (Comparative Example 1) was 50.3 MPa, occurring at 1120℃. Example 2 of this invention added 2 wt.% iron removal slag, increasing the peak intensity of sample S2 to 55.3 MPa and earlier to 1090℃. Example 1 of this invention added 4 wt.% iron removal slag, further significantly increasing the peak intensity of sample S4 to 57.2 MPa and significantly earlier to 1080℃.

[0071] It can be seen that the present invention achieves a dual optimization effect by adding 2-4% of iron removal waste residue: on the one hand, it increases the ultimate flexural strength of ceramic products by 10-14%; on the other hand, it significantly reduces the sintering temperature required to obtain this peak strength by 30-40℃ compared with the prior art.

[0072] Figure 3 Furthermore, it can be seen that, using 40 MPa as the acceptable standard, the present invention, compared to the prior art without the addition of iron removal slag (Comparative Example 1), enters the acceptable range at a lower temperature (1060℃). This indicates that the present invention not only has advantages in pursuing the limits of material performance, but also effectively reduces the difficulty of production control and energy consumption costs in actual production.

[0073] The flexural strength test results strongly demonstrate the technical advantages of this invention: the strength-temperature curves of all samples show a trend of first rising and then falling, but the addition of iron removal slag significantly changed the position and height at which the peak strength was reached. This indicates that iron removal slag, as a highly efficient sintering aid, can achieve significant energy saving and consumption reduction while ensuring excellent product performance by promoting the densification process at low temperatures.

[0074] (4) Shrinkage rate: During the sintering process, ceramic materials undergo a series of physicochemical changes, such as the volatilization of gases inside the material, oxidative decomposition reactions, melting of fusible materials to form a liquid phase, and tight bonding between particles. These changes ultimately lead to changes in the size of the ceramic material.

[0075] The difference in length dimension before and after the sample firing process ( R a - R b ) and the length of the sample before drying R a The ratio R s The percentage (%) is called the firing shrinkage rate, and its calculation formula is shown below:

[0076] In the formula, R s Indicates the shrinkage rate (%) of the material. R a The length of the material before firing. R b This refers to the length of the material after firing.

[0077] like Figure 4 The linear shrinkage rate test results show that the maximum shrinkage temperature of samples S2 and S4 (with added iron removal slag) of this invention is shifted forward to approximately 1100℃, confirming the promoting effect of iron removal slag on low-temperature sintering of ceramics. Although the maximum shrinkage value of the composite ceramic is slightly reduced, this, along with the bulk density data, points to the same conclusion: the optimal mechanical properties of the material can be achieved at low temperatures (e.g., 1080℃), while higher temperatures will lead to over-firing and a decrease in the density and strength of the material, thus precisely defining the low-temperature, high-efficiency process window of this invention.

[0078] Table 2. Firing shrinkage rate (%) of ceramic products at different sintering temperatures

[0079] As shown in Table 2, the firing shrinkage rate of all samples increased with increasing sintering temperature, indicating that heating promoted the densification process of the green body. Compared with the control group without added iron removal slag, the samples with 2% and 4% slag had relatively lower shrinkage rates at the same temperature. This may be because the introduction of slag increased the initial bulk density of the green body, thus achieving a similar densification effect with less shrinkage. Notably, the shrinkage rate (7.69%) of Example 2 (2% slag) at 1100℃ was very close to the shrinkage level of the control group at higher temperatures, while the shrinkage rate of Example 1 (4% slag), although generally lower, showed a significant increase in the 1080–1100℃ range, indicating that its sintering activity increased with increasing temperature. This result, along with data on bulk density, flexural strength, and other properties, confirms that iron removal slag can effectively promote green body sintering at lower temperatures, while providing a wider process window for product size control.

[0080] (5) Whiteness: The sintered ceramic products were processed into 440mm diameter, flat, unglazed discs using a whiteness tester. Before testing, the sample surface was wiped with a clean, soft cloth to ensure it was free of dust contamination.

[0081] Three measurement points, P1, P2, and P3, are determined at the center of each ceramic disc specimen and at both ends along a diameter direction 200 mm from the center. The whiteness meter is then aligned closely with these three predetermined measurement points in sequence, and the whiteness value at each point is recorded. W 1, W 2, W 3.

[0082] The whiteness value of a single ceramic specimen is the arithmetic mean of the whiteness values ​​at its three measurement points. W avg The calculation formula is as follows:

[0083] In the formula, W avg The average whiteness of the material. W 1, W 2, W 3 represents the whiteness values ​​corresponding to the three selected measurement points.

[0084] After measuring multiple samples of the same formulation, the final reported whiteness value of the formulation sample is the average of the values ​​of all samples. Specific results are shown in Table 3 and... Figure 5 As shown.

[0085] Table 3. Whiteness (%) of ceramic products at different sintering temperatures

[0086] As shown in Table 3, increasing the amount of iron-removing slag added resulted in a decrease in the whiteness of the samples at the same sintering temperature. However, the whiteness values ​​of Examples 1 (sample S4) and Example 2 (S2) of the present invention, at sintering temperatures ranging from 1060℃ to 1080℃, exceeded the usage requirements (whiteness value 22%). This indicates that the whiteness of the samples obtained by adding 2-4 wt.% of the iron-removing slag in the present invention, at sintering temperatures ranging from 1060℃ to 1080℃ in the low-temperature zone, meets the usage requirements.

[0087] like Figure 5 As shown, the whiteness values ​​of all samples with added iron removal slag (Examples 1-3 of this invention) fluctuated between 20.79 and 23.25 when the sintering temperature was below 1100℃. Compared with the comparative example without added slag (22.36), the whiteness decreased slightly, but the overall difference was not significant. This is because the Fe2O3 abundant in the iron removal slag itself has coloring properties, participates in the reaction during sintering and is contained in the ceramic matrix, thus having a certain impact on whiteness. It is worth noting that as the sintering temperature increased from 1060℃ to 1080℃, the whiteness of the samples in each example showed an upward trend. This may be due to the increased amount of liquid phase generated at high temperatures, which promoted the densification of the green body and thus improved the light reflection effect. When the temperature was further increased to 1100℃, the whiteness of some samples decreased slightly, which may be related to the crystal phase transformation or the change in the valence state of iron.

[0088] (II) Phase and Microstructure Analysis Test method: X-ray diffraction analysis (XRD): Phase analysis of samples using an X-ray diffractometer.

[0089] Scanning electron microscope (SEM): Uses a scanning electron microscope to observe the microscopic morphology of a sample.

[0090] Test Results and Analysis: XRD analysis: In the XRD pattern of Comparative Example 1, only the original ceramic crystalline phases such as quartz and mullite were detected. However, in the XRD pattern of Example 1 (S4-1080) of this invention, in addition to the original phases, obvious characteristic diffraction peaks of fir olivine (Fe2SiO4) and hematite (Fe2O3) appeared (see...). Figure 6 This indicates that the iron-removing slag participated in the reaction during sintering and generated a low-temperature eutectic phase, which explains the reason for the reduction in sintering temperature from a phase perspective.

[0091] SEM analysis: The comparison of the SEM microstructure of Comparative Example 1 (S0-1140, no waste residue added) and Example 1 (S4-1080, 4% waste residue added) reveals the key structural evidence for achieving low-temperature sintering in this invention.

[0092] First, from the low-magnification morphology comparison, it can be seen that after Comparative Example 1 was sintered at 1140℃, its microstructure (such as...) Figure 7 As shown in a), it still exhibits obvious open pores and weak interparticle connections. However, in Example 1 of this invention, sintering at 1080°C (60°C lower) results in a microstructure (as shown in a diagram). Figure 7 (As shown in b) it shows that the particles are more tightly packed and the number of pores is significantly reduced, indicating that its densification level is significantly better than that of traditional high-temperature processes.

[0093] Furthermore, high-magnification SEM images revealed the microscopic causes of the aforementioned macroscopic structural differences. Comparative Example 1 sample (e.g.) Figure 7 As shown in c), the particle surface exhibits numerous wrinkles, a typical characteristic of insufficient surface diffusion during the initial sintering stage. In contrast, the sample from Example 1 of this invention (such as...) Figure 7 As shown in d), the particle surface becomes exceptionally smooth, which is direct evidence that mass transport (especially surface diffusion) is significantly activated during sintering. This morphological feature, combined with the iron olivine (Fe2SiO4) crystals detected by XRD, indicates that the iron removal slag effectively promotes the migration and mass transfer processes by forming low-melting-point compounds.

[0094] (III) Energy Conservation and Economic Benefit Estimation According to national standards (GB 21252, GB / T 2589), energy consumption decreases by approximately 12.5% ​​for every 100℃ reduction in ceramic sintering temperature. Based on this, it is estimated that this invention, by reducing the sintering temperature from 1140℃ to 1080℃ (a reduction of approximately 60℃), will save approximately 7.5% of energy consumption. By using its own waste residue to replace purchased sintering aids, it achieves "zero cost" for sintering aids. Simultaneously, it saves on waste residue transportation, storage, and disposal costs, approximately 1200 yuan / ton. Overall, this invention has significant economic and environmental benefits.

[0095] Based on the performance tests and analysis of the above systems, we can conclude that: This invention successfully reduced the sintering temperature of architectural antique ceramics from 1140℃ to 1060-1100℃ by introducing 2-4 wt.% of ceramic iron removal waste. Test data on bulk density, water absorption, and flexural strength all indicate that the key physical properties of products sintered within this low-temperature range (as in Example 1) meet or exceed the standards of traditional high-temperature (1140℃) sintered products (Comparative Example 2), completely overcoming the technical obstacle of underfiring and performance degradation caused by simply lowering the temperature (as shown in Comparative Example 1).

[0096] XRD and SEM analyses provide a solid scientific basis for the aforementioned macroscopic properties. Specifically, the novel phases detected in the XRD patterns (such as fir olivine) confirm that the iron removal slag formed a low-temperature eutectic phase during sintering, while the SEM images visually demonstrate that the iron removal slag accelerated mass transport, resulting in a highly densified microstructure at low temperatures. These two characterizations together reveal the core mechanism by which this invention reduces the sintering temperature.

[0097] Whiteness testing clearly shows the color change of the product after the addition of iron-based oxides. The ceramic products of this invention are more suitable for use in building ceramics and industrial ceramics where color requirements are not high and functionality is the primary concern. Color deviation is not a drawback; this invention achieves energy saving and iron slag recycling, and is clearly distinguishable from traditional daily-use porcelain technology that pursues high whiteness.

[0098] By adopting this invention, the sintering temperature can be reduced by 40 to 60°C compared to existing methods, resulting in energy savings of approximately 6% to 8%. Simultaneously, the waste residue generated during production can be directly used as raw material, eliminating the need to purchase additives and saving on waste disposal costs. This invention not only achieves high-quality low-temperature sintering in terms of process technology but also demonstrates in principle that a system capable of low-temperature sintering can be formulated using the ceramic iron removal waste residue itself, proving its technical feasibility.

[0099] This invention not only achieves high-quality low-temperature sintering of ceramics at the process level, but also solves the high energy consumption problem of traditional high-temperature sintering of ceramics by utilizing the waste residue generated during the ceramic production process to construct a stable low-temperature eutectic system. It also verifies the scientific feasibility of synergistic realization of solid waste resource utilization and high-quality ceramic production.

[0100] The above-described embodiments are preferred embodiments of the present invention and are only used to facilitate the illustration of the present invention. They are not intended to limit the present invention in any way. Any person skilled in the art who makes local modifications or alterations to the technical content disclosed in the present invention without departing from the scope of the technical features of the present invention shall still fall within the scope of the technical features of the present invention.

Claims

1. A method for producing ceramics by low-temperature sintering of iron removal waste slag, characterized in that, The method includes the following steps: (1) Ingredient mixing: Iron-removing waste residue from the ceramic production process is added to the ceramic raw materials as a sintering aid, mixed evenly, and performance additives and dispersants are added to obtain the mixture; wherein, the amount of iron-removing waste residue added is 2-4 wt.% of the total mass of the ceramic raw materials; (2) Molding: The mixture obtained in step (1) is aged under vacuum for 18-24 hours, and then pressed into shape to obtain ceramic green body for later use. (3) Sintering: The ceramic green body obtained in step (2) is sintered at a temperature of 1060 to 1100°C to obtain ceramic products.

2. The method for producing ceramics by low-temperature sintering of ceramic iron removal waste slag according to claim 1, characterized in that: The main component of the iron removal slag in step (1) is Fe2O3, and the content of Fe2O3 is 30% to 40%. The ceramic raw materials include 0.4% bauxite, 2.5% recycled material, 3% BH material, 4.7% fine ceramic tile powder, 9% fine potassium sand, 1.8% polishing residue and glaze residue, 2% fine edge grinding residue, 2.3% silica sand, 36.6% high-sodium stone powder, 3.6% Jiangxi talc mud, 6.0% mixed bentonite, 11% mixed mud paste, 8.1% Mingchuang high-alumina mud, 4.5% gray-black raw mud, and 4.5% base bentonite.

3. The method for producing ceramics by low-temperature sintering of iron removal waste slag according to claim 1, characterized in that: The performance additives are Yueyang ceramic body reinforcing agent and liquid deflocculant, wherein the amount of Yueyang ceramic body reinforcing agent added is 0.1 wt.% of the total mass of ceramic raw materials, and the amount of liquid deflocculant added is 0.8 wt.% of the total mass of ceramic raw materials. The dispersant is sodium tripolyphosphate, and the amount added is 0.2 to 0.5 wt.% of the total mass of the ceramic raw materials.

4. The method for producing ceramics by low-temperature sintering of iron removal waste slag according to claim 1, characterized in that: In step (1), the iron slag and ceramic raw materials are mixed by ball milling for 8 to 12 hours.

5. The method for producing ceramics by low-temperature sintering of ceramic iron removal waste slag according to claim 4, characterized in that: During ball milling, the mass ratio of the primary material, milling media, and water is 1:1.2 to 2:0.5 to 1. After ball milling, a mixed ball milling material is obtained. The mixed ball milling material is dried at 160° to 200° for 2 to 2.5 hours, then cooled to room temperature. Then, 8 to 12 wt.% of water is added, and the mixture is ground through a 20 to 30 mesh sieve to obtain the lower layer of raw material, which is the mixed material.

6. The method for producing ceramics by low-temperature sintering of iron removal waste slag according to claim 5, characterized in that: In step (2), the mixture dried to a moisture content of ≤0.5% is replenished with water to adjust the moisture content to 7%–9%, ​​and then aged under a vacuum of 0.06–0.08 MPa for 18–24 hours. Through the synergistic effect of moisture swelling and negative pressure, the tiny air bubbles remaining inside the mixture after drying are removed, so that the porosity of the subsequently formed blank is reduced to below 2% and the cracking rate is ≤0.3%. The aging temperature is 25-30℃, and the bubble removal rate is ≥90%, which improves the plasticity uniformity of the mixture by more than 15%.

7. The method for producing ceramics by low-temperature sintering of iron removal waste slag according to claim 1, characterized in that: In step (2), the ceramic green body is formed by pressing with a hydraulic press at a pressure of 20-50 MPa.

8. The method for producing ceramics by low-temperature sintering of ceramic iron removal waste slag according to claim 1, characterized in that: In step (3), the sintering process is atmospheric pressure sintering, the heating rate is 3 to 10 °C / min, and the temperature is held at 1060 to 1100 °C for 0.5 to 2 hours.

9. The ceramic product obtained by the method for producing ceramics using low-temperature sintering of ceramic iron removal waste slag as described in any one of claims 1-8, characterized in that: The ceramic product has a water absorption rate of 0.33-0.97%, a bending strength of 55.3 MPa-57.2 MPa, a shrinkage rate of 6.13-7.64%, and a whiteness of 22.06-23.

35.

10. The application of the method for producing ceramics by low-temperature sintering of ceramic iron removal slag as described in any one of claims 1-9 in the production of building ceramics or industrial ceramics.

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